Smells bad (5)
I believe the answer is:
reeks
'smells bad' is the definition.
(reeking is a kind of smelling bad)
This is the entire clue.
(Other definitions for reeks that I've seen before include "Smells bad" , "Gives off a strong unpleasant smell" , "Smells very strongly" , "Macgillycuddy's - -" , "Is humming" .)